Dairy whey is a byproduct of cheese or casein manufacture. In recent years, disposal of whey has become a major problem for the dairy industry. Past methods of whey disposal, such as introduction into waterways, municipal sewage systems, or land irrigation have proven to be undesirable and are falling under increasing government restriction. Approximately 12% of the solids in whey are proteins. The proteins in whey do not biodegrade easily and largely contribute to the difficulties of whey disposal. Whey proteins also complicate the use of whey in industrial application such as lactose crystallization or production of alcohol. Currently, attempts are being made to remove the protein from whey so that the remainder of the whey can be practically and usefully disposed of.
Unlike most proteins, whey proteins do not markedly demonstrate an isoelectric point, i.e., they do not precipitate out of solution at the environmental pH at which the sum of the electrostatic charges on the protein molecule is zero. Consequently, whey proteins cannot be easily and economically isolated from milk by a simple adjustment of their environmental pH as is done with other proteins. Currently, whey proteins are recovered from milk by heat coagulation or by use of ultrafiltration technology. Neither of the two recovery methods are without their negative points. Heat coagulation of whey proteins only isolates the lactalbumin in whey and yields a denatured, low functionality protein. The ultrafiltration process is quite involved and complex resulting in an expensive protein concentrate which contains significant amounts of the less desirable milk constituents, such as lactose. Ultrafiltered whey protein concentrates find only limited usage due to their expense and narrow range of functional properties. Whey proteins could find more widespread application if whey proteins could be isolated from milk in an undenatured, fully functional form at a practical and economical cost.
The protein isolation process contained in this invention promotes the interreaction of two different forms of protein, enabling the two proteins to be precipitated from suspension at a common, isoelectric pH. It is based upon the concept that if whey proteins, which are not subject to isoelectric pH precipitations, are interreacted with a protein or proteins which are strongly insoluble at isoelectric pH the resultant interreacted protein complex will precipitate out of suspension at the latter protein's isoelectric pH. The present invention uses this protein isolation process to completely react whey proteins with isoelectrically precipitable proteins to form unique protein complexes which can be separated from the whey leaving it essentially free of protein.